Help with designing a rocket nose cone with Von Karman characteristics

[bry0603]

Hello,

I am new to Fusion 360 but have been slowly learning different techniques.  It's great.  My next objective is to find out how to create more complicated conical shapes such as rocket nosecones that have different characteristics.  I'd like to start by making a nose cone with Von Karman profile.  Can anyone help get me started with this?  I can easily make a simple cone but that is about as far as I have been.

Thanks in advance!

[TheCADWhisperer]

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@bry0603 wrote:

I'd like to start by making a nose cone with Von Karman profile.  Can anyone help get me started with this?. 

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What formula would you like to start with?

[davebYYPCU]

Sketch an ellipse, trim to keep one quarter and revolve.

if you have a 3point curve, use the sketch spline snapped to the three points.

Formula based - you can use User Parameters.

Might help....

[bry0603]

I'm having a difficult time just cutting and pasting the formula but here it is in picture form:  I would like a VK series so we would use C=O, R=15 and L=150. Does this help?  Thanks so much for the help!

[Anonymous]

Hey @bry0603 although I am not the resident expert here, two plugins immediately come to mind: Fusion Sheeter and SwiftCalcs.  @prainsberry created Sheeter to link design parameters with Google sheets.  I think it might do the trick here, with Sheets doing the heavy lifting on the math heavy side to generate x-y coordinates to drive your loft or revolve.  Check out his work here.  If that doesn't work you might consider SwiftCalcs, super cool plugin very similar to the likes of MathCAD.  I haven't used either tool extensively but could be worth looking into.

[bry0603]

Thanks @Anonymous.  I have installed the plugin, made a spreadsheet that can generate the x and y coordinates for the 2D nose cone but I can't get much further than that.  I will have to reach out to the maker of that plugin and watch some tutorial vids tomorrow but I'll plug away on this and report back. 

Open to other ideas as well.

Thanks!

[bry0603]

Here is where I am with the Sheeter addin.  Not very far at all!  I have the coordinates for 1/2 of the 2D nose cone.  I am hoping to get a sketch using those and then revolve.  @prainsberry do you have any suggestions on where to go from here?  Thanks in advance.

[TheCADWhisperer]

Do the coordinates in your spreadsheet make logical sense?

[bry0603]

I think they do NOW.  The resolution isn't quite what I want but should work for this experiment.

[TheCADWhisperer]

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@bry0603 wrote:

I think they do NOW.  The resolution isn't quite what I want but should work for this experiment. 

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I think that you might find that fewer points return better curve than more points.

Can you zip and attach your spreadsheet here - I would like to experiment a bit, but not motivated enough to build it (the spreadsheet) myself.

[bry0603]

Does this work for you?

[prainsberry]

Hey actually i don't think this is a good use case for Sheeter.  There is a script that will import XY coordinates and fit a spline.  I believe it is in the app store.

[bry0603]

@prainsberrythanks for your input.

[HughesTooling · Accepted solution]

ImportSplineCSV is supplied with Fusion, just click Add-Ins on the toolbar. I think it needs XYZ coordinates so just add a column of zeros.

Mark

[bry0603]

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@HughesTooling wrote:

ImportSplineCSV is supplied with Fusion, just click Add-Ins on the toolbar. I think it needs XYZ coordinates so just add a column of zeros.

Mark

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Eureka!  That did it.  For some reason I had to divide all my values by 10 to get it to scale and import correctly but we made some progress there!  I used the ImportSplineCSV to get my main spline line and then built the inner line to spec or close enough and then just used revolve.  Awesome!  Thank you!

[chrisplyler]

I manually drew out to 75mm, then got tired of the monotony...

[TrippyLighting]

Please check the curvature on that spline!

[chrisplyler]

I already closed the file without saving, and I'm not drawing it again. You're wife told me you've got too much curvature on YOUR spline.

[HughesTooling]

@bry0603 You could have created a solid cone then used a shell feature to make it hollow or did you want a nonuniform thickness?

Mark

[Anonymous]

@bry0603 I found sheeter to be a great option.  My f3d file and screencast are attached. If possible I will share the Google Sheets directly, send me an email at Ricky.Huff@synapse.com and I can link you to it.